Process for preparing cocondensates of aspartic acid amines

ABSTRACT

A process for preparing cocondensates of aspartic acid and amines by heating aspartic acid and amines in the presence of acidic catalysts comprises supplying the feed region of the extruder with particulate aspartic acid and a downstream metering zone with at least one amine and at least one acidic catalyst, condensing the resulting mixture to such an extent by heating that the downstream end of the extruder discharges a precondensate which contains at least 20-95% by weight of the starting aspartic acid in condensed form, and then completing the condensation of the precondensate. The cocondensates are useful as incrustation inhibitors in detergents.

This application is a 371 of PCT/EP97/03751, filed Jul. 14, 1997.

The present invention relates to a process for preparing cocondensatesof aspartic acid and amines by heating aspartic acid and amines in thepresence of acidic catalysts while mixing at up to 300° C. in anextruder.

WO-A-94/01486 discloses the preparation of modified polyaspartic acids.According to one version of the disclosed process, mixtures of asparticacid and a comonomer which has at least one functional group arepolycondensed at from 100 to 270° C. Examples of suitable comonomers arefatty acids, polybasic carboxylic acids, anhydrides of polybasiccarboxylic acids, alcohols, amines, alkoxylated alcohols and alkoxylatedamines. The polycondensation is effected in the presence of acidiccatalysts, for example phosphoric acid, hydrochloric acid or sulfuricacid. The polycocondensates are used as additives in washing andcleaning compositions, for example.

WO-A-96/05241 discloses a process for preparing polyaspartic acid bypolycondensation of finely divided aspartic acid at above 150° C. in thepresence of acidic catalysts. It is not until the reaction zone that theacidic catalysts first come into contact with the aspartic acid whichhas been heated to at least 150° C. The acidic catalysts are preferablysprayed onto the surfaces of the fine aspartic acid particles in such away that no tacky solutions are produced thereon. This avoids theformation of an aggregated or clumped polymer mass.

Prior DE application 19 517 715.0, unpublished at the priority date ofthe present invention, discloses a process for preparingpolycocondensates of aspartic acid by adding a catalytic acid and atleast one comonomer to a hot aspartic acid at 150-210° C. in such a waythat the formation of tacky solutions is avoided. The cocondensation ispreferably effected in a fluidized bed.

EP-A-0 644 257 discloses a process for the thermal polycondensation ofaspartic acid in the presence of acidic catalysts. The polycondensationcan optionally take place in the presence of polyfunctional monomerssuch as diamines or polyamines. It is effected within the temperaturerange from 110 to 300° C. under intensive mixing of the reactants, forexample in a single- or multiple-screw extruder. The product obtained isa finely divided, optionally modified, polyaspartic acid containing morethan 80% of the starting aspartic acid in condensed form.

The above-described processes have the disadvantage that aminecomonomers give rise to particularly tacky reaction masses which arevery difficult to handle.

It is an object of the present invention to provide an improved processfor preparing cocondensates of aspartic acid and amines.

We have found that this object is achieved by this invention by aprocess for preparing cocondensates of aspartic acid and amines byheating aspartic acid and amines in the presence of acidic catalystswhile mixing at up to 300° C. in an extruder, which comprises supplyingthe feed region of the extruder with particulate aspartic acid and adownstream metering zone with at least one amine and at least one acidiccatalyst, condensing the resulting mixture to such an extent by heatingthat the downstream end of the extruder discharges a precondensate whichcontains at least 20-95% by weight of the starting aspartic acid incondensed form, and then completing the condensation of theprecondensate at from 150 to 300° C.

The aspartic acid used can be L-, DL- or D-aspartic acid or a mixturethereof. The aspartic acid can have any desired crystal size and crystalform. The average particle diameter of the aspartic acid crystals can befor example from 0.01 to 5, preferably from 0.1 to 2, mm.

The finely divided aspartic acid is condensed with primary, secondary ortertiary amines. Preference is given to using alkylmonoamines having upto 100 carbon atoms in the alkyl chain. Particular preference is givento primary and secondary alkylmonoamines having from 1 to 30 carbonatoms for use as cocondensable compounds. Examples of such amines aretallow fatty amine, hydrogenated tallow fatty amine, octylamine,2-ethylhexylamine, nonylamine, decylamine, 2-propylheptylamine,undecylamine, dodecylamine, tridecylamine, cetylamine, stearylamine,palmitylamine, oleylamine, coconut fatty amine, mono-α-branchedsecondary amines, bis-α-branched secondary amines of the general formulaR⁴ R³ HC--HN--CHR¹ R², where R¹, R², R³ and R⁴ are each independently ofthe others substituted or unsubstituted C₁₋₂₀ -alkyl.

The amount of amine used per mole of aspartic acid extends for examplefrom 1 to 40, preferably from 1 to 20, % by weight.

Examples of suitable acidic catalysts include phosphoric acid,phosphorous acid, phosphonic acids, diphosphoric acid, triphosphoricacid, more highly condensed phosphoric acids, sulfuric acid, ammoniumhydrogen sulfate, sodium hydrogen sulfate and potassium hydrogensulfate. In some cases, mixtures of acidic catalysts have advantages.For instance, low melting mixtures of ammonium hydrogen sulfate, sodiumhydrogen sulfate and potassium hydrogen sulfate or mixtures of sodiumhydrogen sulfate and potassium hydrogen sulfate are used. Also suitableare trimethylammonium hydrogen sulfate and triethylammonium hydrogensulfate as acidic catalysts. Particular preference is given to usingphosphoric acid. The amount of acidic catalyst used per mole of asparticacid ranges for example from 1 to 40, preferably 5 to 30, % by weight.Particularly preferred cocondensates are prepared by cocondensation ofaspartic acid with tallow fatty amine and phosphoric acid.

The cocondensation is carried out in a two-stage process. In the firstprocess stage, aspartic acid, amine and acidic catalyst are mixed in anextruder by input of mechanical energy. For this purpose, the feedregion of the extruder is supplied with particulate aspartic acid and adownstream metering zone with at least one amine and at least one acidiccatalyst. The mixing of the components can be effected at from 20 to250° C., preferably at from 50 to 150° C. The input of mechanical energyinto the system and the heat of neutralization released in the course ofthe coming together of amine and acidic catalyst serve to heat up themixture. The mixture is condensed to such an extent by heating to thecondensation temperature, which ranges for example from 150 to 300° C.,preferably from 180 to 280° C., that the downstream end of the extruderdischarges as a precondensate containing at least 20-95% by weight ofthe starting aspartic acid in condensed form. The condensation ispreferably carried on to such an extent that the downstream end of theextruder discharges a precondensate containing at least 40% by weight ofthe starting aspartic acid in condensed form. Depending on the degree ofcondensation, the downstream end of the extruder discharges reactionmixtures which have the consistency of viscous melts or--if the degreesof condensation are above 40%--are solid even under the temperatureconditions of the condensation and are present in the form of friable,nontacky materials.

The cocondensation is preferably effected continuously by supplying theextruder with the starting materials batchwise or continuously and thedownstream end of the extruder discharging the same amount ofprecondensate. The residence time in the extruder depends on the levelof condensation product (=degree of condensation of the aspartic acid)desired in the precondensates. The residence times of the reactionmixture in the extruder range for example from 0.1 to 30, preferablyfrom 0.2 to 10, min.

In the second process stage, the precondensates obtained in the firststage are condensed to completion. The degrees of condensation achievedfor the aspartic acid are then more than 98%, preferably 100%. Thecondensation in the second process stage is preferably effected byheating the precondensates, distributed over a heated surface, at from150 to 300° C., preferably at from 180 to 250° C., for from 0.5 to 300,preferably from 1 to 120, min. Suitable equipment for this operationincludes for example heating belts, kneaders, mixers, paddle dryers,extruders, rotary tube furnaces and other heatable apparatus in whichthe condensation of solids can be carried out by removal of water ofreaction.

The condensation in the first stage and the postcondensation in thesecond stage can be carried out at atmospheric pressure, undersuperatmospheric pressure or else under reduced pressure, for examplewithin the pressure range from 1 to 200 mbar. The components arepreferably condensed under atmospheric pressure. The postcondensation ispreferably carried out on a heatable belt by applying the precondensatethereto, for example in a layer thickness of from 0.1 to 10, preferablyfrom 0.5 to 5, cm and heating at from 150 to 300° C., preferably at from180 to 250° C., to complete the condensation. The degrees ofcondensation in the second process stage are dependent on the selectedtemperature, the residence time and the degree of condensation of theprecondensate. In the second process stage, the degree of condensationof the precondensate is increased. The entire aspartic acid can becondensed, so that the degree of condensation is 100%. However, it issimilarly possible to set degrees of condensation in the second processstage which range from 69 to 99%, preferably from more than 95 to 100%.The aspartic acid not condensed into the cocondensate can be extractedfrom the cocondensate by washing with water or with dilute acids.However, it may also remain in the polycondensate. This procedure ispreferred for practice in industry. To work up the cocondensates, theyare extracted with from 1 to 10 times, preferably from 1.5 to 4 times,the amount of water and thereafter, in the form of a slurry in water,hydrolyzed at for example pH 8-10 by addition of sodium hydroxidesolution. This converts the succinimide units of the cocondensates intosodium aspartate units. The salts of polyaspartic acid are soluble inwater. The cocondensates will contain from 0.1 to 20, preferably from0.5 to 10, % by weight of phosphorus when phosphorus acids are used. Thecocondensed phosphorus compounds are not water- or base-extractable fromthe cocondensate.

The cocondensates prepared by the process of this invention are veryeffective incrustation inhibitors in detergents. They are particularlyuseful for manufacturing detergents which comprise less than 25% byweight of sodium phosphate, calculated as trisodium polyphosphate, orwhich are phosphate-free. The cocondensates prepared by the process ofthis invention are preferably used together with zeolites formanufacturing phosphate-free detergents. The detergents comprise forexample from 0.2 to 10, preferably from 0.5 to 5, % by weight of thecocondensates.

The percentages in the Examples are by weight, unless otherwiseindicated.

EXAMPLES

The feed region of an extruder was meteringly supplied with L-asparticacid having a particle size of about 0.5 mm in diameter and thesubsequent metering zone of the extruder separately with molten tallowfatty amine and 75% strength aqueous phosphoric acid. The quantitiesused in each example are shown in the table. The metering zonetemperature was 80° C. In the downstream heating zone of the extruderthe mixture was heated to 200-270° C. At the extruder outlet theprecondensate was obtained either as a soft paste or as a hard, friablemass. The residence time of the reaction mixture in the extruder wasadjusted by varying the throughput. Condensates prepared at from 250 to270° C. and throughputs from 2.3 to 5 kg/h were solid and friable evenin the hot state. Notwithstanding the high temperatures, the condensatesremained pale yellow.

To determine the degree of condensation, the cocondensates were washedwith water and the insoluble residue was determined. The experimentallydetermined polycondensate quantity was expressed as a proportion of thearithmetically expected polycondensate quantity (degree of condensationon exit from extruder in % of theory).

The reaction conditions and the degree of condensation are reported inthe table. The cocondensate in Example 1 had a soft tacky consistency onexit from the extruder. Examples 2 to 9 produced a hard friable product.

To complete the condensation of the precondensates prepared in the firstprocess stage, 100 g of each of the precondensates was heated at 180° C.for one hour. Thereafter the degree of condensation was determined bymeans of the above-described extraction. The condensates had molarmasses M_(w) of about 8.000 (determined by the light scattering method).

                                      TABLE                                       __________________________________________________________________________       Phosphoric                                                                          Tallow           Degree of                                                                           Degree of                                        acid fatty Temperature  condensation condensation                             [%], amine at  on after                                                       based on [%], extruder Through- exit from heating                            Ex. aspartic based on outlet put extruder at 180° C.                   No. acid aspartic acid [° C.] (kg/h) [%] [%]                         __________________________________________________________________________    1  20    10    200   5.46 55    100                                             2 15 5 200 5 60 100                                                           3 15 5 250 5 64 100                                                           4 15 5 250 5 61 100                                                           5 15 5 250 2.5 70 100                                                         6 15 5 270 2.5 76 100                                                         7 20 10  250 2.73 80 100                                                      8 20 10  270 2.73 94 100                                                      9 7.5 5 270 2.3 50  69                                                      __________________________________________________________________________

We claim:
 1. A process for preparing cocondensates of aspartic acid andamines comprising:a) mixing and heating particulate aspartic acid andamines up to 300° C. in the presence of an acidic catalyst, anddischarging a product which contains at least 20-95% by weight of thestarting acidic acid in condensed form; b) condensing said dischargedproduct obtained in a) by heating at 150 to 300° C.
 2. The process ofclaim 1, wherein the mixing is in a extruder and the extruder comprisesa feed region that is supplied with particulate aspartic acid and adownstream metering zone which contains at least one amine and at leastone acidic catalyst.
 3. The process of claim 1, wherein the asparticacid is selected from the group consisting of L-aspartic acid,D,L-aspartic acid, D-aspartic acid, and mixtures thereof.
 4. The processof claim 1, wherein the amine is alkylmonoamine.
 5. The process of claim1 wherein the amine is selected from the group consisting ofhydrogenated tallow fatty amine, octylamine, 2-ethylhexylamine,nonylamine, decylamine, 2-propylheptylamine, undecylamine, dodecylamine,tridecylamine, cetylamine, stearylamine, palmitylamine, oleylamine,coconut fatty amine, mono-α-branched secondary amine, bis-α-branchedsecondary amines of the general formula:

    R.sup.4 R.sup.3 HC--HN--CHR.sup.1 R.sup.2

where R¹, R², R³, and R⁴ are each independently substituted orunsubstituted C₁₋₂₀ alkyl, and mixtures thereof.
 6. The process asclaimed in claim 2, wherein the metering zone of the extruder issupplied separately with primary or secondary alkylmonoamines and acidiccatalysts selected from the group consisting of phosphoric acid,phosphorous acid, phosphoric acids, diphosphoric acid, triphosphoricacid, more highly condensed phosphoric acids, sulfuric acid, ammoniumhydrogen sulfate, sodium hydrogen sulfate, potassium hydrogen sulfateand mixtures thereof.
 7. The process as claimed in claim 1, wherein theamine is from 1 to 40% by weight per mole of aspartic acid and theacidic catalyst is from 1 to 40% by weight per mole of aspartic acid. 8.The process as claimed in claim 1, wherein the amine is from 1 to 20% byweight per mole of aspartic acid and the acidic catalyst is from 5 to30% by weight per mole of aspartic acid.
 9. The process as claimed inclaim 1, wherein the amine is tallow fatty amine and the acidic catalystis phosphoric acid.
 10. The process as claimed in claim 1, wherein theproduct in a) contains at least 40% by weight of the starting asparticacid in condensed form.
 11. The process as claimed in claim 1, whereinthe condensing in b) is on a heatable belt in a layer thickness of from0.1 to 10 cm with heating at 150 to 300° C.
 12. The process of claim 11,wherein the heating is from 180 to 250° C.